A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head transducer (also referred to as a “read/write head” or simply “head”) which is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head, which is housed in a slider, and the surface of a magnetic-recording disk must be tightly controlled. Suspensions have a spring-like quality which biases or urges the air bearing surface (ABS) of the slider against the disk to enable the creation of the air bearing film between the slider and disk surface. An actuator relies in part on the suspension's force on the slider and on the aerodynamic characteristics of the slider ABS to provide the proper distance between the read/write head and the surface of the magnetic-recording disk (the “flying height”) while the magnetic-recording disk rotates. A slider therefore is said to “fly” over the surface of the magnetic-recording disk.
An HDD includes at least one head gimbal assembly (HGA) that generally includes a slider that houses the head, and a suspension. Each slider is attached to the free end of a suspension that in turn is cantilevered from the rigid arm of an actuator. Several semi-rigid arms may be combined to form a single movable unit, a head stack assembly (HSA), having either a linear bearing or a rotary pivotal bearing system. The suspension of a conventional disk drive typically includes a relatively stiff load beam with a mount plate at the base end, which subsequently attaches to the actuator arm, and whose free end mounts a flexure that carries the slider and its head. Disposed between the mount plate and the functional end of the load beam is a “hinge” that is compliant in the vertical bending direction (normal to the disk surface). The hinge enables the load beam to suspend and load the slider and the read/write head toward the spinning disk surface. It is then the job of the flexure to provide gimbaled support for the slider so that the read/write head can pitch and roll in order to adjust its orientation.
The flexure in an integrated lead suspension is generally made out of a laminated multilayer material. Typically, it consists of a support layer (e.g., steel), a dielectric insulating layer (e.g., polyimide), a conductor layer (e.g., copper), and a cover layer (e.g., polyimide) that insulates the conductor layer. The electrical lead lines are etched into the conductor layer, while the polyimide layer serves as the insulator from the underlying steel support layer. The steel support layer is also patterned to provide strength and gimbaling characteristics to the flexure. The conducting leads, called traces, which electrically connect the head transducer to the read/write electronics, are often routed on both sides of the suspension, especially in the gimbal region. Normally the traces consist of copper conductor with polyimide dielectric insulating and cover layers but no support stainless steel layer and only provide the electrical function. The primary mechanical support function is provided by the flexure legs (e.g., steel) which normally run adjacent to the traces.
Increasing areal density has led to the necessary development and implementation of secondary actuators for improved head positioning through relatively fine positioning, in addition to a primary voice coil motor (VCM) actuator which provides relatively coarse positioning. Some hard disk drives employ micro- or milli-actuator designs to provide second stage actuation of the recording head to enable more accurate positioning of the head relative to the recording track. Milli-actuators are broadly classified as actuators that move the entire front end of the suspension: spring, load beam, flexure and slider. Micro-actuators are broadly classified as actuators that move only the slider, moving it relative to the load beam, or moving the read-write element only, moving it relative to the slider body.
However, micro-actuator mechanisms and designs that are not perfectly collocated with slider assemblies, when driven, often times excite unwanted modes of vibration. These excited modes, involving other structures (e.g. loadbeam) in addition to the microactuator and slider itself, can lead to significant head offtrack. Since these modes often times are at frequencies lower than the primary microactuator mode, resulting servo bandwidth may be compromised.